package general_tips;

import java.util.BitSet;

public class SimpleBloomFilter {

    private static final int DEFAULT_SIZE = 2 << 24;// 布隆过滤器的比特长度
    private static final int[] seeds = new int[]{7, 11, 13, 31, 37, 61}; // 这里要选取质数，能很好的降低错误率

    private BitSet bits = new BitSet(DEFAULT_SIZE);
    private SimpleHash[] func = new SimpleHash[seeds.length];

    public static void main(String[] args) {


        SimpleBloomFilter filter = new SimpleBloomFilter();
        System.out.println(filter.contains("crankzcool@gmail.com"));

        filter.add("crankzcool@gmail.com");
        filter.add("crangzcool@gmail.com");
        filter.add("cranmzcool@gmail.com");
        filter.add("cranbzcool@gmail.com");

        System.out.println(filter.contains("crangzcool@gmail.com"));
        System.out.println(filter.contains("cranmzcool@gmail.com"));
        System.out.println(filter.contains("crannzcool@gmail.com"));//误判了
        System.out.println(filter.contains("cranbzcool@gmail.com"));
    }

    public SimpleBloomFilter() {
        for (int i = 0; i < seeds.length; i++) {
            func[i] = new SimpleHash(DEFAULT_SIZE, seeds[i]);
        }
    }

    public void add(String value) {
        for (SimpleHash f : func) {
            bits.set(f.hash(value), true);
        }
    }

    public boolean contains(String value) {
        if (value == null) {
            return false;
        }
        boolean ret = true;
        for (SimpleHash f : func) {
            ret = ret && bits.get(f.hash(value));
    }
        return ret;
    }

    public static class SimpleHash {
        private int cap;
        private int seed;

        public SimpleHash(int cap, int seed) {
            this.cap = cap;
            this.seed = seed;
        }

        public int hash(String value) {
            int result = 0;
            int len = value.length();
            for (int i = 0; i < len; i++) {
                int letter=value.charAt(i)-96;
                result=letter*seed;
                seed*=seed;
//                result = seed * result + value.charAt(i);
            }
            return (cap - 1) & result;
        }
    }
}